Hyperovulation and the genetics of twins

in StemSociallast year (edited)

For kid lovers, the appearance of cute little twins is always a sight to behold. I have seen several ladies jokingly attesting that their ovaries tingle each time they see a set of twins, especially if they are identical. I would not really know if ovaries do tingles. Perhaps my female audience can clear me up on this.

By MultipleParent - Image:TwinsTwins.JPG, CC BY-SA 3.0

Somewhere in a small town in one of the states in Southwestern Nigeria, Oyo-state to be precise, almost every households boast of at least, a set of twins. The phenomenon is prevalent so much in this town to the extent that it has been labeled as the twin capital of the world. A research carried out as far back as 1972 to 1982 revealed an average of 45 to 50 sets of twins out of every 1000 births in the town. The town is known as 'Igbo Ora' and the people attribute this condition to 'an act of God'.

Several inquiries have been made into what might be responsible for the unusually high rate of twins in the town with the strongest evidence pointing to the consumption of a particular species of yam by the women of the town. The research conducted by fertility experts linked the presence of a high amount of phytoestrogen in a species of yam in the town to hyperovulation in women, and hence, the high prevalence of twin births. However, some experts in the same field have debunked the claims and opined that there are no foods that increase the chances of giving birth to twins.

The biology of twin

The biology behind the formation of a twin is best explained based on the type of twins. There are basically two types of twins based on phenotypic appearance.

  1. Identical twins
  2. Fraternal twins
Identical twins generally look like each other in every way, except for the differences that can be attributable to environmental factors. Hence, identical twins might appear a bit different due to the effect of the environment where they grow, especially if they do not grow up in the same environment. They are formed from a single fertilized egg and hence, are usually of the same sexes and also genetically identical. A fertilized egg divides into two and each egg grows to become identical babies.

Fraternal twins, on the other hand, do not look like each other and can be of the same or different sexes. They are formed from two different eggs that get fertilized by different sperms and hence, are both phenotypically and genotypically different from each other.

One interesting thing about fraternal twins is that they can be given birth to days, weeks, or even months apart. Normally, twins are usually given birth to minutes apart, or sometimes, just a few hours apart. While the likelihood of identical twins being given birth to days apart is very slim or even non-existence, history has recorded cases of fraternal twins being given birth to several days apart due to a condition known as uterus didelphys.

The condition is characterized by a woman having two uteri with each uterus having its own cervix. Each uterus is capable of carrying a pregnancy, meaning that, if fertilization takes place at different times within each uterus, the result would be babies given birth to at different times. A good illustration of this case was witnessed when a 29-year old woman gave birth to a set of twins that are 11 months apart.

Hyperovulation and the genetics of giving birth to twins

My wife and I always joke about having a set of twins and each time, we always refer to the fact that my dad being a twin might be a deciding factor. We, along with several other people, obviously think that giving birth to twins might be genetic. Perhaps we are right.

Whether giving birth to a twin is based on genetic or otherwise depends largely on the type of twin. The formation of identical twins is largely due to chance and has nothing to do with genetics. The division of a fertilized egg/embryo in the uterus resulting in identical twins is a random event that happens based on pure chance.

However, the same cannot be said for fraternal twins. Like I had pointed out earlier, the formation of fraternal twins depends on the release of two eggs, a condition known as hyperovulation. This condition is generally known to be genetic. However, since the male sex does not have eggs, hyperovulation is only witnessed in females but males can pass on the gene to their female offspring.

It thus means that without hyperovulation, the chances of having a fraternal twin are zeros and with hyperovulation, having fraternal twins becomes a thing of genetics. If there is no history of hyperovulation in the lineage of a woman the chance of her having a fraternal twin is zero while the chance of having an identical twin is purely random. Having a twin has nothing to do with a man, except that a man can be a carrier for hyperovulation gene to his daughter, resulting in her having a good chance of producing fraternal twins.


The phenomenon of giving birth to a set of twins has been found to have nothing to do with lifestyle as reported in some quarters. However, it can be genetic if the twins are fraternal or unidentical. Identical twins happen by pure chance and result from the random division of the embryo into two. Fraternal twins can only happen when two eggs are released simultaneously from the ovary of a woman, a phenomenon known as hyperovulation. Hyperovulation is a heritable trait that only manifests in the female sex, a man can only be a carrier. Hence, the formation of fraternal twins depends largely on the genetic history of a woman's lineage. Some women have a medical condition that results in them having two uteri, thus enabling them to carry two babies that can also be referred to as twins. This kind of twin can be given birth do days, weeks, or even months apart.

Final words

Before calling it quit for this session, I will like to ask you, my audience, what is the maximum number of twins have you witnessed a woman given birth to? I am talking about real life, not the one read in the news. Personally, I have seen a woman that gave birth to 6 sets of twins. The woman has 13 children in total with only the firstborn being a single birth.

Thank you all for reading.





As always, a fascinating article not only interesting but full of information. This article caught my eye because I have identical twin brothers. Their births were separated by 15 minutes, but that was a very dramatic 15 minutes. This was long time ago (mid 1940s), when prenatal checkups were not so much the thing...not for everyone, anyway. My mother did not know she was carrying twins, and the doctors who assisted at the delivery were also surprised. The second twin was delivered with great difficulty and suffered permanent injuries. Many years later, I learned that the syndrome of a surprise second twin with injuries was not extraordinary. While twins are a blessing, I think the argument for prenatal care cannot be made too strongly.
Thank you for another great article.

 last year (edited)

15 minutes between twins? Oh I thought this would be faster. Interesting! And I can imagine the stress of the second twin not being delivered!

And let's avoid even discussing the 11months stuff of the post!!

You're right...it was a long time. Too long. Today there would be imaging to show the position of the twins (or that there were in fact twins!). A C-section would have been performed when the second twin was seen to be in a compromised position. Back then, panicked doctors frantically used forceps to reposition the baby and facilitate delivery. This resulted in great harm.
Can't say enough about proper prenatal care.

We are living with the strengths and weaknesses of our era. We discussed the cons in another post already :(

Well, thanks to technological advancement nowadays. Most people know when they are carrying multiple babies and there are sophisticated processes to ensure safe deliveries. Although accidents do occur sometimes, I must confess.

Thanks for taking your time to read through.

Yep, the advances helped us to be able to monitor those things better. We have learned a lot in the meantime. This is our fate: learning, and hopefully understanding :)

Amazing and interesting piece baba. I once read about the history of Igbo Ora (the twin capital of the world) and I was wowed.
Meanwhile, the story of the woman giving birth to twins that are 11months apart is nothing short of amazing and fascinating.
I've also read about twins from different fathers, now that's weird.

I would even have difficulties to imagine them as twins as they won't look the same due to the age difference.

Exactly my thoughts too. Should we just call them siblings? :)

I would!

The twin from different fathers is explainable if the woman has two uteri. Fertilisation can take place at different times in the two uteri by sperms from different persons because each uterus has its own cervix.

Interesting article!! Just like "Igbo Ora", there is a village in India named "Kodinhi" where almost every family gave birth to a pair of twins.
I myself have seen a woman giving birth to just 2 sets of twins when I was posted in the gynecology department.
About the village, I don't think food plays any major role, genetics might be the key.

Would be interesting to know if those twins in igbó ora and Kodinhi are fraternal, identical, or a mix of the two. If there are identical twins, it will throw up an interesting hypothesis to research on. Bùt I really doubt. Just wondering why there are limited research into these incidence of high twins in some places when compared to others.

I was about to say the same as @gentleshaid. Is there any study made on the village?

It's a mix of two actually,
it was during an oral hygiene camp in 2016 I guess, more than 50 pairs of twins showed up. Doctors were surprised and later found out, more than 350 pairs of twins were living there in the population of just 2000.
Sadly, i couldn't find a single research paper on this topic.

 last year (edited)

Too bad no one undertook any research on that... But well... it is what it is. Thanks for the specifications.

A very interesting post! :) Thank you for sharing

You are welcome

Personaly, I have seen Just 4.

Alot of myths circulate about twins.

I once heard that it is due to some drugs the lady takes thus distabillising her reproductive cycle.

Some hormonal drugs such as clomid actually induce the release of multiple eggs during ovulation, leading to not just twins, but other multiple births such as triplets, quadriple, etc. Several people with multiple births beyond twin have confessed to taking hormonal drugs, usually as an effort restore irregular monthly flow.

@tipu curate

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My granddaughters were triplets: a single and identical twins.

That's really lovely and another interesting angle to look at. The most likely explanation would be that there were fraternal twin at the onset and then one of the fraternal twins divided into two while still at embryonic stage to form an identical twin. Is there a history of fraternal twin in your family?

My sweeties are adopted, so I don't know.

Oh..thats lovely. I guess we will only know with time.

that's some interesting information! Especially that I have a twin sister and we have big chances to have twins when we create our families :)

Nice! are you guys identical? If not, then you just might also give birth to twins.

More or less. Of course, to us, it looks like we are very different but most of the people don't see the differences 😅


Lovely. You guys look perfectly alike. I had an identical twins as friends while I was in school. For four years, I could distinguish their differences. Even till now.

You definitely look the same :)

Thanks :D

Wow so nice to read! Giving birth to twins with 11 months in between... Fascinating! I would love to have twins but I guess you never know. Conceiving is genetic lottery lol

Well, unless the gene for fraternal twins is somewhere in your family or you have two uteri, you can only depend on mother nature to smile on you. In that case, you will be getting identical twins.

Absolutely amazing post. Learnt quite a bunch of new stuff here. thanks for sharing

You are welcome. We will continue to learn until we die.


exactly boss! Our brains were never built to stop working.. It woks till death, so does learning!

Ahaha! I cannot help you with the tingling ovary stuff. More seriously, I thought that the probability of having twins was actually connected to genetics. Fortunately, I was partly right (I even paused the reading of your post to google that ;) ).

Thanks for the write-up!